1. Field of the Invention
This invention relates to brake oil pressure controlling valve devices for use on automotive vehicles or the like.
2. Description of Prior Art
As is known, a valve device of the kind concerned is arranged in an automotive brake system in order to obtain a satisfactory braking effect by restraining oil pressure rise in the rear wheel brakes as occurring when the brake pedal is depressed and the inertial mass of the vehicle body shifted forwardly, reducing the effective loads on the rear wheels, thereby to prevent the wheels from being locked. The known form of such valve device includes a control valve inserted in the brake oil line interconnecting the brake master cylinder and the rear wheel brakes and operable in response to the vehicle deceleration exceeding a predetermined value to reduce the level of oil pressure being transmitted to the rear wheel brakes to a level substantially below that of the oil pressure output from the brake master cylinder.
For such operation responsive to vehicle deceleration, the brake oil pressure controlling valve device generally includes a weighted valve element arranged in a valve chamber inserted in the brake oil line intermediate the ends thereof and movable to close the valve port in response to the vehicle deceleration exceeding a predetermined value. This arrangement, however, has previously involved some problems. First, when the vehicle runs down a steep slope, the weighted valve element is apt to misoperate and impair the braking performance, hindering any proper rise of oil pressure in the rear wheel brakes. Secondly, the time of action of the valve element is variable with the speed of brake application due to the dynamic effect upon the valve element of the pressure oil from the brake master cylinder flowing into the valve chamber. This causes the upper limit valve of the oil pressure being transmitted to the rear wheel brakes to change and thus makes it difficult to obtain the brake performance desired.